The basic principle of ultrasonic welding is to convert high-frequency electrical energy into high-frequency vibration mechanical energy. This reciprocating vibration is transmitted to the thermoplastic or metal, creating friction and heat at the plastic-to-plastic, plastic-to-metal, or metal-to-metal interface. In ultrasonic welding, friction generates heat that fuses the surfaces of two materials.
Ultrasonic welding system has a variety of configuration options, including different frequencies (15Khz-50Khz), different power (600W-4800W), and various forms, such as pneumatic ultrasonic welding machines, servo ultrasonic welding machines, handheld welding machines, non-standard welding machine, metal ultrasonic welding machine and so on.
Many factors affect the success of ultrasonic welding: mold (including upper horn and lower bottom die), frequency, material, weld design, welding parameters and part injection molding, etc.
1. Welding System Frequency
Typical ultrasonic welding system frequencies are 15Khz, 20Khz, 30Khz, 35Khz and 40Khz. The appropriate welding frequency needs to be selected based on product size, type, strength, and appearance requirements. Generally, you can refer to the following principles:
For the welding of small and precision electronic products (including PCB boards and microelectronic components) casings, use a high-frequency 40Khz welding machine. The amplitude of the 40Khz welding machine is smaller and the welding pressure can be minimized, which can avoid damaging the internal electronic components of the product.
For small products with high requirements on appearance. Use a 40Khz welding machine for welding because its amplitude and pressure are small and the welding accuracy is higher.
For welding medium-sized and large-sized parts, use low-frequency 15Khz or 20Khz welding machines.
The 20Khz welding machine is suitable for welding most products of small to medium sizes and is also the most widely used ultrasonic frequency at present.
2. Materials
For ultrasonic welding of plastics, only thermoplastics are suitable for welding. Because they can be melted within a specific temperature range.
Thermosetting plastics degrade when heated and cannot be welded using ultrasonic waves.
3. Plastic Welding Structure Design
The most critical factor affecting ultrasonic welding is the welding structure design. When a part is in the design stage, engineers should carefully consider and evaluate it. Welded structures come in a variety of designs, each with its own characteristics and advantages. Which design to choose depends on the plastic type, part geometry, welding requirements, injection molding capabilities, and appearance requirements.
To determine which weld design is suitable for your product, please consult the ultrasonic manufacturer engineer or sales staff.
4. Positioning Molds and Welding Horn
Welding horn materials can be selected from aluminum alloy, titanium alloy, and hard alloy steel. The mold materials can be aluminum alloy, stainless steel, and resin mold. How to choose materials generally requires consideration of plastic-type, material glass fiber content, welding structure and size, welding strength, and service life. For example, to extend the life, a hard alloy steel welding horn is the best choice.
A good welding horn design has symmetry and uniform output amplitude. In order to increase the wear resistance of the welding horn and extend its service life, the surface of the welding horn can be treated with tungsten carbide or chromium plating. The molds can be designed in sections to better fit the product.
5. Welding Parameters
During the welding process, welding parameters will affect the welding results. These parameters include amplitude, welding pressure, trigger pressure, welding distance, and welding energy.
Different types of plastic require different amplitudes. Welding pressure can be adjusted via a knob or software settings. Trigger pressure means that when the welding head presses the product and the pressure reaches a certain set value, the device starts to send ultrasound. This value can be adjusted through software settings.
There are several control methods for the ultrasonic welding process:
Time welding mode is setting the duration of ultrasonic welding.
Distance welding mode (position welding mode) sets the distance or position of welding.
Energy welding mode is to set the energy of welding.
Different welding modes are suitable for different products. You can monitor all parameters during welding, set parameter ranges for qualified parts, and reduce the unqualified rate.
Plastic ultrasonic welding is a special process. In the early stages of product development, you should cooperate with the ultrasonic equipment manufacturer and use the equipment manufacturer’s experience in this field to evaluate the product structure and weld design and conduct welding tests on the samples. To improve the qualification rate of subsequent mass production.
